Material characterization of AlGaN/GaN based HEMT structures

• Main Author: Nur Hidayat Bin Hatwi
• Other Authors: K Radhakrishnan
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/60792
• Institution: Nanyang Technological University

Group–III nitride semiconductors are viewed as the next-gen materials due to the high potential in optoelectronic and microelectronic applications. This is based on nitrides having properties such as high mobility and high velocity of the electron-carriers. HEMTs (high electron mobility transistors) have excellent properties such as high voltage tolerance and high power characteristics, hence enabling them to be used in a wide range of applications. The purpose of this project is to characterize AlGaN/GaN based HEMT structures grown by molecular beam epitaxy. Data will be analyzed to decide on the most ideal conditions and dimensions of HEMT so as to fully exploit its capabilities. Techniques such as Hall, Capacitance-Voltage, Current-Voltage and Atomic Force Microscopy will be used to obtain the experimental data. The analysis of the results will be based on a variety of HEMT characteristics, which will then be correlated to the film growth parameters such as metal flux levels and the layer structure of each sample. Data seemed to suggest that AlGaN/GaN based HEMT structures, with a GaN-buffer layer that is lightly doped with carbon (20mTorr to 40mTorr) and not having a spacer layer, showed better two-dimensional electron gas characteristics. The average mobility of these samples (V717, V719 and V725) was recorded to be 649 cm-2/Vs, sheet resistivity was 1102 Ω-cm and carrier density was 9.3×1012 cm-3. The average mound size was 3.47 nm in height and 0.55 µm in width. Vertical leakage currents ranged from 10-9A to 4×10-8 A. Certain growth conditions have been identified as optimal, and future experiments could involve varying the thickness of the epilayers in order to produce even more proficient HEMTs.